I've been using jab a lot lately.
It's a good tool to condition the opponent, you can combo into other jabs, dash grab, nair and even dash attack at kill percent. (~140 jab1>jab2>buffered dash attack)
The thing is, after you condition your opponent that you'll go for a grab after the jab1>jab2, you can shield instead at higher percents when they pop up a bit more if you expect a combo breaking aerial, fsmash if they like air dodge after it, and a charged fsmash on faster fallers that will tend to spot dodge.
Lately I've been using it as a starter for rising dair which by itself actually combos into many things since it's hard hit with it in other ways other than at the edge or from a laggy attack (at which case you should simply rest oos)
Remember however that jab is not safe on shield, so try going for it when an opponent runs towards you for a grab at a point where you'll both most likely try to throw out a quick move, or combo into it from a late nair hit or fair at low-mid percents and over.
